Investments In and Advances To Affiliates - Summarized Financial Information (Details) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Nov. 15, 2017	Jul. 25, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Revenue			$ 2,643	$ 2,693	$ 2,613	$ 2,581	$ 2,660	$ 2,639	$ 2,452	$ 2,530	$ 10,530	$ 10,281	$ 11,260
Operating margin			643	642	625	554	632	691	556	501	2,464	2,380	2,663
Net income (loss)			(1,286)	$ 261	$ 150	$ 98	(693)	$ 229	$ (387)	$ 74	(777)	(777)	762
Assets, Current			6,398				6,416				6,398	6,416
Liabilities, Current			6,028				5,277				6,028	5,277
Liabilities, Noncurrent			21,402				24,365				21,402	24,365
Stockholders' Equity Attributable to Noncontrolling Interest			2,380				2,906				2,380	2,906
Stockholders' Equity Attributable to Parent			2,465				2,794				2,465	2,794
Undistributed Earnings Of Minority Owned Affiliates Included In Retained Earnings			254								254
Distributions Received From Minority Owned Affiliates											69	24	18
Basis Difference Between Carrying Amount And Investment			46								46
Minority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue											762	586	641
Operating margin											165	145	152
Net income (loss)											72	64	210
Assets, Current			418				308				418	308
Assets, Noncurrent			5,372				2,577				5,372	2,577
Liabilities, Current			633				626				633	626
Liabilities, Noncurrent			2,629				1,209				2,629	1,209
Stockholders' Equity Attributable to Parent			2,527				1,048				2,527	1,048
Majority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue											16	23	24
Operating margin											5	9	11
Net income (loss)											(15)	(2)	$ 6
Assets, Current			70				16				70	16
Assets, Noncurrent			102				181				102	181
Liabilities, Current			10				10				10	10
Liabilities, Noncurrent			147				122				147	122
Stockholders' Equity Attributable to Parent			$ 15				$ 65				$ 15	$ 65
sPower [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 19	$ 461